An information system of an enterprise that provides various services (for example, a system that manages a usage fee of communication facilities involved in connection between telecommunications carriers of respective cellular phones) stores data in a storage system such as a RAID (redundant arrays of inexpensive discs) to enhance reliability of data used at the time of providing services. This storage system is provided with various data protection functions and by, for example, periodically inspecting errors of each HDD (hard disc drive) provided in the storage system, forestalls problems such as a loss of data.
There are two types of errors occurring to a conventional storage system; the error attributable to a recording medium of the HDD and the error not attributable to the recording medium. As to a method of detecting the error attributable to the recording medium, the error is detected by, for example, writing test data to the recording medium and checking whether the written test data may properly be read out.
On the other hand, with respect to the method of detecting the error not attributable to the recording medium, there are methods such as the method of giving attention to I/O (input/output) of the HDD with a low processing load and, in the case of occurrence of a delay in a response time to such HDD, determining that the error has occurred to the HDD to which the response delay has occurred and the method of determining that the error has occurred when there is a bias in I/O access to the HDDs in a RAID group.
Japanese Patent Application Laid-open No. 5-298132 discloses a method of avoiding the error by determining whether to blockade a part in which the error has occurred from the number of times of occurrence of the error, the frequency of occurrence of the error, and the interval of occurrence of the error. Further, Japanese Patent Application Laid-open No. 2001-265538 discloses a technology of performing an inspection with respect to a plurality of inspection items and forecasting the error that can occur to the disc from a combination of inspection results.
However, the above conventional technologies had a problem of erroneously detecting the error not attributable to the recording medium of the HDD and erroneously detecting a normal HDD as an abnormal HDD.
For example, in the method of detecting the error based on the delay in the response time, there has been a case in which, when the HDD's self-diagnosing processing and data access compete with each other, data processing is performed after the self-diagnosis and as a result, the occurrence of the response delay is erroneously detected and the normal HDD is detected as the abnormal HDD.
In the method of detecting the error based on the bias of the I/O access, in the case of a random I/O where it is possible that the data access temporarily concentrates on a particular HDD, there has been a problem of erroneously detecting the occurrence of the response delay and detecting the normal HDD as the abnormal HDD.
The above erroneous detection of the normal HDD as the abnormal HDD may be reduced by changing a threshold for determining as the response delay but in this case, conversely, it becomes difficult to reliably detect the abnormal HDD.
As seen above, in the present state, the conventional technologies, unable to accurately detect the error not attributable to the recording medium of the HDD, are not capable of properly determining whether the HDD is normal.